1. Field of the Invention
This invention relates to a rotary coupler for signal transfer between a rotor and a stator and, more particularly to a rotary coupler for a rotary magnetic head type video tape recorder or the like.
2. Description of the Prior Art
In a rotary magnetic head type video tape recorder, a rotary transformer is extensively utilized for the transfer of recording video signal and reproduced video signal to and from a rotary magnetic head provided in a rotor.
FIG. 1 shows a well-known rotary transformer. The rotary transformer illustrated includes a rotor 1 and a stator 2 which are made of ferrite. Primary and secondary coils 3 and 4 are provided in grooves formed in the outer and inner peripheries of the rotor 1 and stator 2, respectively. These coils 3 and 4 are magnetically coupled together for signal transfer.
In this rotary transformer, two pairs of primary and secondary coils 3 and 4 are provided for two channels. The rotor 1 and stator 2 are provided with respective metal rings 5 and 6 received in respective grooves. These metal rings 5 and 6 shield the two channels from each other. Leads 7 and 8 are led out from the coils 3 and 4 for connection to an external circuit.
In the rotary transformer which utilizes magnetic coupling between coils for the signal transfer, the bandwidth coverage is narrow because of the inductance of the coils and floating capacitance, and the upper frequency limit is 60 MHz at the most. Recently, with the development of digital VTRs, data recorders, high quality television sets, etc., there is a trend for increasing bandwidth coverage, and there is a demand for a rotary coupler having wide bandwidth transmission characteristics.